In English, they asked a man sitting beside my friend if he could direct them. The man answered them in Japanese, saying he did not understand English. The Americans, who clearly spoke no Japanese, repeated slowly 'Tokyo station', but the man was not trying to understand, and ignored them.
My friend then intervened, and told the two Americans where they would have to change trains. They thanked her politely. A successful episode of inter-cultural communication.
But suddenly the man sitting beside my friend piped up and tore into her for her insolence in speaking to the foreigners in English. It was an outrageous humiliation for him that a mere woman should show off her English in front of others and make him look stupid. The tirade of insults lasted some time, as the man tried to vent some of his fury at having lost face.
Dumbfounded at this attack for doing nothing more than helping a pair of strangers, my friend sat silent until the outraged man got off the train. The real problem was that he had understood what the two Americans wanted to know. All Japanese spend six years learning English at secondary school. But the stress is on drumming in as many vocabulary lists as possible, with little emphasis on the spoken language.
Foreigners in Japan for the first time find it strange that often no one will dare to sit beside them in a train or on a plane. The reason is not that foreigners are regarded as smelly or as a potential source of disease - it is just the fear from the Japanese side that the foreigner might address them in a foreign language, with all the pitfalls of embarrassment that opens up.
The man on the underground was simply too embarrassed to speak a few words of badly pronounced English to the Americans, so he preferred to pretend he could not speak a word of English. It is the privilege of anyone to decline to speak a foreign language if he or she so chooses. But to criticise others for communicating with foreigners in their own language is another matter.
Japanese exchange students who return to their schools after a year or more overseas - usually in the United States - are frequently discriminated against in class for speaking English too well. The reason is often that they speak the language better than their teachers. Noboru Takeshita, a former prime minister, was once an English-language teacher, but when he led the government he was famously unable even to say 'Hello' to visiting dignitaries in English.
The shortcomings in the system of English teaching have often been pointed out. But the conservative Ministry of Education is loath to change much. In one respect there has been an improvement: more schools are employing native English-speakers as teaching assistants. But these teachers all report their frustration in not being able to get a discussion going in class, because the pupils are accustomed to listening to their teacher without speaking up or asking questions. So the amount of spoken English the foreigners can pass on is still limited.
Some institutions are taking the English-language problem more seriously. An experimental university north of Tokyo in Tsukuba has just told its first-year students that they will have to sit an in-house English exam, which is harder than the standard Ministry of Education version, and actually includes a section on aural comprehension.
Many budding young salarymen with an internationalist leaning get up early once or twice a week these days to go to English classes, trying to pick up at work what they could not learn while at school. The number of Japanese trying to study overseas is also increasing - currently about 120,000 young people are studying in foreign colleges every year.
But even the outward exodus is not without its problems. According to the records of students taking the Test of English as a Foreign Language (TOEFL) in the US for the two years from July 1989, more Japanese than students from any other nation took the test. But the average score of Japanese students made them 149th of 162 nationalities.
TOEFL scores can range from 677 to 200, and a score of 550 is required to enter most US and Canadian universities. Japanese students' average score was 484, ranking below the average proficiency of applicants from Cambodia, Laos, Afghanistan, Mongolia and 144 other countries. Perhaps the bureaucrats from the Education Ministry should consider a study trip to Kabul or Ulan Bator to see how they could improve English-language courses in Japanese schools.